Within TWS, you can check a contract’s description either by double-clicking on a market data line or by right-clicking on a market data line and selecting Financial Instrument Info followed by Description. You can see the extended contract details by selecting Financial Instrument Info followed by Details. This option will open a web page showing all available information on the contract.
Whenever a contract definition is provided via the TWS API, the TWS will try to match the given definition to a single contract. This mechanism allows for significant flexibility since it gives the possibility to define the same contract in multiple ways.
The vast majority of stocks, CFDs, Indexes or FX pairs can be uniquely defined by providing the symbol, security type, currency and exchange. More complex contracts such as options and futures require extra information.
For further information, please see the documentation.